Automatic regulating device



Dec. 2o, 1933. C, M- DENMS 2,140,933

AUTOMATIC REGULATING DEVICE Dec. 20, 1938. c. M. DENNIS AUTOMATICREGULATING DEVICE Filed Aug. 20, 1954 5 Sheets-Sheet 2 Filed Aug. 20,1934 5 Sheets-Sheet 5 Uff Off

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(Muervr De. 20, 1938. c. M. DENNIS 2,140,933

AUTOMATIC REGULATING DEVICE Filed Aug. 20, 1934 5 Sheets-Sheet 4INVENTOR.

Dec. 20,1938.

C. M. DENNIS AUTOMATIC REGULATING DEVICE Filed Aug. 2o, 1954 5shets-sheet 5 INVENTOR.

Patented Dec. 20, 1938 UNITED STATES PATENT OFFICE Application August2t,

'av claims.

My invention relates to improvements in automatic devices :forregulation and control of heating, chemical process operations, and manyother operations in which it is desired either to main- 5 tain certainvalues constant, to change them in predetermined amount, or at apredetermined rate. it includes improvements by which the operation ofexisting control devices may he made more uniform and less subject toerror. It also includes improved methods and apparatus for theelectrical measurement of temperature, which maybe advantageously usedin conjunction with other apparatus of my invention in the regulation ofheating and cooling operations.

In connection with all control devices, and the heat or other variablequantity which is to be regulated, there is a time lag betweenoccurrence of the change which requires compensation, and thecompensating response of the control apparatus. During this period oflag a further change may occur, and the total amount of 'compensatingresponse required is correspondingly increased. A similar conditionexists .after response ultimately causes return to the control point.Lag of control operation causes the desired value to be not only reachedbut exceeded, and a continuous hunting, values, results. The time lagand amount of such hunting varies with the nature vof the variable to becontrolled, and with the nature of the devices used for regulation. Insome cases it is not objectionable; in most cases, however,objectionable fluctuations from desired control may result.

The type of objectionable hunting which is encountered in a wide varietyof industrial control problems may, for convenience, be described inconnection with the familiar example of irregular temperature controlgained in a residence when the furnace is controlled by an ordinarythermostat. This irregularity is especially marked when heating iseffected by means of a coal fired steam furnace. This may be illustratedby reference to Fig. 1, which shows in somewhat exaggerated form thetype of heating curve resulting when furnace drafts are turned on in themorning, after furnace has been shut off and the house temperature hasdropped say, to 60 F. during the night. The furnace drafts are turned onat time a, but there is an appreciable interval before the fire beginsto burn strongly enough to generate steam, and a further interval beforedistributing pipes are warmed and radiatorslstart to heat. Actual risein room temperature therefore may not begin until time b. With theradiators hot the room temperature rises with above and below desired.

1934, Serial No. '140,586

(Cl. 23d-*74) increasing rapidity until the control temperature of isreached at c and the thermostat causes the furnace drafts to close. Theresidual heat of re and radiators causes the temperature to continuerising, however, until a maximum of, say, 74 is reached at d, afterwhich the temperature slowly falls until the thermostat operates toagain open the furnace drafts at e. By this time re and radiators willhave cooled to such extent that heat will not be immediately supplied.The hunting cycle of undercooling and overheating will continue throughf, g, h, etc., in decreasing amount but with increasing frequency, untila minimum fluctuation, which varies with the equipment and conditions,is reached.

A somewhat similar behavior results when control devices now in commonuse are utilized for regulation of chemical and industrial processes,as, for example, regulation of proportional flow of an alkali tomaintain exact neutralization of an acid flow which is subject to suddenvariations. Lag in operation of a pH meter and motor controlled valvesmay permit large excesses or deflciencies to accumulate, with resultantundesirable hunting and delay before stability at the desired value isagain reached.

Referring again to Fig. 1, it is apparent that if the original approachto the control temperature had been anticipated, and the furnace draftsfirst shut off at some suitably chosen point 7', the residual heat fromthe furnace and radiators would have been just sufficient to causecontinued temperature rise along the broken line, :1L-k, until thedesired temperature was reached but not exceeded at k. Similarly, if thefurnace was turned on at some point Z, as the temperature was droppingfrom'too high a value, the necessary heat would be supplied by the timepoint m was reached. In any given installation the location of thesuitable points y' andl will vary at different times, depending to alarge extent upon the rate at which the' temperature is rising orfalling. In mild weather, for example, the rate of heating Will be rapidand cut-off temperature 1 should be lower than in cold weather, when therate of heating is slower and residual heat will cause less subsequenttemperaturerise. Similarly, if the desired control temperature has forany reason been exceeded, the rate of cooling will be relatively l'ow inmild weather and the on point, l, should be lower than would bedesirable in cold weather. Similar relations exist during approach tcdesired values in control of acidity and in regulation of otherindustrial operations.

I have discovered means by which requirements of changing demand orapproach to desired control values may be largely anticipated, and theamount of anticipation made to vary with the rate of change and, to acontrolled extent, With the amount of excess or deciency to becompensated for. The basis of this part of my invention may beillustrated by means of Figs. 2 and 3. If all points of Fig. 2 are on ahorizontal plane surface, and a is a Weight attached to a string, L -b,then as b is moved along the line A-B through successive positions b', betc., the weight will follow through successive positions a, a along atractrix curve. In theory the curve approaches the line A-B as a limitbut reaches it only at infinity. In practice the distance from theweight to the line A-B becomes negligible at some point as c, afterwhich the Weight will follow along the line. During the above the anglewhich the string makes with the line A-B becomes progressively smalleruntil it is substantially zero at c. The true equation of the tractrixcurve is complicated, but the following simple equation is approximatelycorrect for that part of the curve in which we are interested.

If the distance which b travels along the line A-B is represented by Iv,the distance of a from A-B by ZI, and the length of the string by m,then in which n is a constant times a:

X (n: insa) The foregoing approaches closely to the tractrix curve afterthe angle a', b', A is less than about 30, from which it follows thatthere is a certain unit of travel of the point, b, which willapproximately halve the distance of a from A-B each time it is repeated.The foregoing formula and statement are included here only to facilitateunderstanding of the operation of the invention to be described.

In Fig. 3, assume that A-B and C-D are parallel lines on a horizontalsurface, and that E--G is a metal rod supported on the surface by asmall wheel, E, and a movable pivot, F, which moves at a constant speedfrom left to right. Further assume that the lines A-B and C-D correspondto the 60 and 70 temperature lines of Fig. 1, and that the position ofpivot F in relation to these lines varies with the actual temperature ofthe room which is under control, while at the same time the constantrate of motion from left to right is maintained. If the temperaturestarts to rise at a fairly rapid constant rate, the pivot F will movealong some line as F-H, through successive positions 1, 2 and 3. Thewheel, E, will follow along a tractrix curve, EJ, lagging behind themotion of the pivot, while the free end of the rod, G, will lead themotion of the pivot toward the control temperature line, C-D, and willcross this line at the point K while the pivot is at point 3corresponding to a temperature of, say, 66. If suitable contacts arearranged to cause the furnace to be shut off when the end of the rod, G,crosses C-D, the point 3 will correspond to the point y' of Fig. l andapproach to the control temperature of 70 will have been anticipated by4.

If the rise in temperature should take place at a slower uniform ratethe pivot would move along some line as F--L and, because of the moreacute angle at which this crosses C-D, G would not cross C-.D, andshut-off contact would not be made, until the pivot reached point 4corresponding to some temperature higher than 3, say 68. In this case,because of slower heating rate, approach to the control temperaturewould be anticipated by only 2 when the shutoff contact was made. Underideal conditions, with the control perfectly adjusted to the constantsof the heating Ysystem, the residual heat of the latter would in eithercase be just suin'cient to cause further temperature rise to 70 afterthe furnace was shut olf, as indicated by curved line 3-M. If there wasno residual heat, and the rise of room temperature stopped at 66 afterthe furnace was shut off, then the pivot would start to move along theline toward N, the drag wheel would start to approach this line along atractrix curve, and the free end of the rod, G, would fall below C-D andagain turn the furnace on. This process would repeat itself causingtemperature to rise until the control temperature of 70 was reached.

If, on the other hand, the residual heat had been so great as to causeoverheating, the pivot would move with room temperature along the line3-6. The drag wheel would follow and, on a descending temperature, wouldcause G to cross C--D and turn the furnace on when pivot.

was at point @corresponding to some temperature above 70.\ In this casethe furnace would have been shut off at the temperature of point 3,turned on at the temperature of point 6, with anticipation of bothdecreasing and increasing heat requirements.

Study of Fig. 3 Will show that for a given rate of temperature rise theamount of anticipation will depend upon a combination of factors. If therate at which the pivot F is moved from left to right is increased, theeffect will be the same as though the rate of temperature rise wasdecreased, that is, there will be less deflection of the arm and lessanticipation. If the distance between E and F is relatively small, thecurvature of the tractrix followed by E as the temperature changes willbe relatively sharp and E will, within a short distance of travel,approximately follow the path of the pivot. In this case the angle whichE-G makes with the line C-D will be chiefly determined, except for smallchanges, by the rate of change of temperature. If the distance between Eand F is relatively large, then the tractrix path of E will only slowlyapproach the line along which the pivot moves. The anticipating lead ofrod end G will in this case be chiefly proportional to the amount oftemperature change, at the outset, and the rate of change will becomethe principal controlling factor only after this rate has continued forsome little time. For any angle of E-G,'the amount of anticipation isdirectly proportional to the length of F-G.

From the foregoing it becomes apparent that there is considerablelatitude in the design of a control, to operate in the manner described,to meet the requirements of different control problems. With suitablevariations some of which will be indicated, this principle may beadapted to control of many variable quantities besides heat, such asacidity. pressure, speed, etc., and is further adapted to control ratesof change independently of absolute quantity. In the illustration whichhas been given, for example, control contacts could be so mounted as tomove with the pivot, F, and cause the furnace to be shut 0E or turned onwhen the rate of heating or cooling exceeded a certain value, regardlessof the temperature. It further becomes apparent that by suitable choiceof constants, including the speed at which pivot F moves from left toright, control may be gained over changes which take place slowly, overmany hours, or rapidly, during a fraction of a second. Choice ofconstants must be determined by average operating conditions for eachapplication. Theoretically perfect control will seldom be gained, butapparatus designed to employ the principle whichhas been described has awide range of llexibility, and in most applications will virtuallyeliminate the objectionable hunting described in connection with Fig. l.Special devices to expedite stabilization at desired control values, andfor other purposes, will be described in connection with speciiicdesigns of control apparatus.

The various designs and combinations of apparatus to be described showsuitable applications of the foregoing principles, but many otherdesigns may be employed to give similar results. My invention includesthe principles, as well as the speciiic designs and combinations, whichare described.

Fig. l together with Figs. 5 and 6 shows in semi-diagrammatic form acontrol apparatus employing the principle which has been described. Acylinder l attached to shaft 2 revolves on fixed bearings. The cylinderis revolved at constant speed in the direction of the arrow through gearchain 4 from shaft Ei, which is connected to a small synchronous motorM1, as for example an electric clock motor. Rolling on the surface of Iis a small wheel, Il, which revolves freely in bearings, 1, in theforked end of a bar, 8. The latter is attached to shaft 8 which pivotsfreely in bearings of support 4I5 which is attached to a base ofinsulating material, Ill. A bronze spring 20 (Fig. 6) makes electricalcontact from I5 to 8 through 9. Attached to the end of 8 is a flexiblebronze strip I9 which makes contact with metal plates II or I2 mountedon an insulating support.

The insulating base I4 is attached to a metal block, IE (Fig. 6) throughwhich screw I1 passes in a threaded hole. The screw I1 revolves freelyin fixed bearings, supports the assembly I4, I5 and I6, and at the sametime moves it from left to right in relati-on to cylinder I, or viceversa, depending upon the direction of rotation of the screw. Attachedto the end of I1 is a cog wheel, 2|. A double ratchet, 22 is attached tothe end of bar 23 which rocks in pivot 24 on the upper end of bar 21(Fig. 5). This bar is supported on hinge 29, attached to the base, 28and is connected through link 3U from pin 3| to the crank 32 whichrevolves continuously with the cylinder drive gears. As 5 turns, the bar21, and the assembly attached to it, are continuously rocked back andforth in a direction normal to the axis of screw I1.

A solenoid coil 2S, having a divided winding is mounted on 21. An ironplunger is centrally suspended in the solenoid by wire 25 hanging fromthe end of bar 23. When no current is ilowing in either half of thesolenoid the spring 33 holds both teeth of the ratchet out of contactwith the cog wheel 2|, as the ratchet is moved back and forth with therocking of 21. If current flows in the lower half of the solenoid theright hand end of 23 (Fig. 5) will be pulled down, the lower ratchetwill be brought into contact with the teeth of 2|, and 2| will be causedto revolve in a clockwise direction. If current flows ence to control oftemperature.

only in the upper half of the solenoid, wheel 2| will be moved in acounterclockwise direction. Depending upon the direction of rotation of2| and the screw I1 to which it is attached, the block I6 and theassembly attached to it will be moved to the left or td the right inrelation to cylinder I.

Attached to I4 is a flexible contact strip, I8, which makes contact witha wire wound resistance coil, I9. If the latter is incorporated in asuitable circuit for the electrical measurement of temperature, pH,etc., and the solenoid is connected to engage the ratchet in onedirection or the other when the circuit is out of balance, the contactI8, and the assembly to which it is attached, will be moved as necessaryto restore balance. The measuring circuit will be selfbalancing and theposition of I8 on Iii will vary with the temperature or other variablewhich is being measured or controlled. Limit switches, which would berequired in practice, are not shown. p

As contact Iii is moved the pivot d will be moved correspondinglyo Theweight of bar 8 and wheel d, aided by light tension on contact spring IUwill keep the wheel from slipping sideways on the surface or thecylinder l, if this is of suitable material, and, because of lesserfriction, the end of ill which is in contact with II or I2 willtherefore move in the same direction as I8 but at a faster rate. lf, asindicated above, the resistance I9 is connected in suitable circuit witha device sensitive to changes in the variable quantity being regulatedand if the contacts II and I2 are suitably connected with means forincreasing or decreasing the supply of corrective agent, we then havemeans of automatically duplicating the regulating conditions which werediscussed in connection with Fig. 3 with refer- The wheel 6 of Fig. 4corresponds to E of Fig. 3, 9 corresponds to F and I0 to G.

Closing of low temperature contact 53 similarly causes I4 etc. to movetoward the right. Adjacent and local to the thermostatic element is asmall electrical resistance heater, 51, which is partly in series andpartly in parallel with resistance I9 through contact I8 which isattached to base I4. Resistance I9 and external resistance 58 are inseries with each other and connected across suitable terminals oftrans-- former 55 or other suitable source of current. As contact I8 ismoved toward the left the amount of current bypassed from I9 through 51will decrease, and vice versa. Within limits determined by suitablechoice of resistance values, and voltage applied, there is some positionof contact I8 on resistance I9 which will cause to flow in heater 51 anamount of current just suicient to warm thermostatic unit 50 to thetemperature at which it will engage neither contact 54 nor contact 53.When the temperature of the medium being regulated is sufficient tomaintain this open contact position, no heat is required in 51 and thistemperature is the upper limit of the range of regulation. The lowertemperature limit of regulation is that at which the current flowing in51 when I8 engages the extreme right end of I9 is just sufficient -toheat 50 to the open contact position. Values arek so chosen that whenthe tractrix contact I0 is at mid position between II and I2, while thedram arm is normal vto the axis of the drum, I, the position of I8 on I9will be such that heat supplied through 51 will be just sufficient tomaintain 5 0 at open contact poall sition between 53 and 54 when thetemperature of the controlled medium is at the desired level.

M2 is a motor or other suitable means for increasing or decreasingsupply of heat from a main source. When I0 engages I2 current will besupplied to Mz through conductor 65, from 34 through the tractrx arm andcontact I0 to I2, and conductor 64 to cause heat supply to be increased.When I 0 engages II a similar circuit will be closed through theconductor 63 to cause heat to be decreased.

In operation the effect of any change in the temperature of thecontrolled medium is to cause either contact 53 or 54 to close, therebyoperating solenoid 26, ratchet and cog wheel 22 and 2|, and screw I'I tomove contact I8 on resistance I9 in the direction and amount necessaryto alter the heat in 51 until 5D is again in midposition, thusconstituting a self balancing temperature measuring circuit. Pivot 9 ofthe tractrx drag arm is also mounted on the same moving base I4 withcontact I 8, and moves in the same amount and direction. If we assumethat the temperature of the controlled medium is substantially below thedesired level, then I4 and the assembly mounted thereon will be in aposition well to the right of that shown, and I0 will be in contact withI2, causing increase in main heat supply. As the temperature risesdecreasing heat from 51 will be required to hold 50 in open contactposition, and I4, etc., will automatically be moved toward the left,moving contact I8 and pivot 9 by like amount. The drag wheel, 6, incontact with revolving drum I will lag behind the lateral motion of thepivot, thereby causing contact I0 on the other end of the drag arm tolead the motion of I8 and 9, whereby it will engage the off contact, II,and shut off the main source of heat before the control temperature hasbeen reached.

At the start of the temperature rise the arms 8 and I0 will have made anincreasing angle with its original position as the wheel 6 followedmotion of 9, in an approximate tractrx path on the drum. With acontinuous and uniform temperature rise this angle increases until itreaches equilibrium at a value determined by the rate of change oftemperature and the surface speed of the drum, I. With other factorsconstant the time and temperature change before the equilibrium angle isreached will vary with the distance from I to 9, but changing the lengthof the drag link does not alter the nal equilibrium angle. After theequilibrium angle is reached the point of contact of I 0 with H-or I2will lead the position of I8 by a fixed amount determin d, together withthe angle of the drag link, by the rate of change.

If the balancing circuit is so adjusted that at a temperature of 70contact I0 just touches the on-oi point when the drag link is normal tothe axis of I, then as the temperature rises from some lower value thiscontact will lead the temperature rise and cause the heat to be shut oifat less than 70. As the rate of heating is decreased the equilibriumangle of the drag link will decrease. Revolution of cylinder I willcause the drag link and contact t0 swing toward normal position. If theinstrument has been exactly adjusted to the overrunning caused byresidual heat in the heating system, this swing will be balanced by thecontinued but slowing movement of 9 to the left, and contact will stayslightly on the off side until the temperature reaches 70, after whichit will turn on or off as necessary to maintain that temperature. If theresidual heat is insuicient to bring to control temperature, the oncontact will be made and repeated as necessary until control temperatureis reached. If for any reason the temperature rises above 70 the draglink will follow, with the drag wheel constantly tracing varying tractrxcurves as it seeks equilibrium with changing rates and positions, andwithin a short period the drag link will be normal to the axis of thecylinder, in a position to the left of the control point, so that thecontact will again lead as the temperature drops,

and the heat will be turned on while the temperature is above 70.Anticipation in varying relation to the rate and amount of change isthus gained.

It will be noted by reference to the tractrix curve of Fig. 2 that therate at which the drag angle decreases falls off greatly as the nalequilibrium position is approached. In the apparatus of my inventionthis is ordinarily of no consequence, since it is usually best practiceto not fully compensate for the lag in response of heating equipment,etc., and the control may be so adjusted that this lag ordinarily causesthe control point to be reached and very slightly overrun after each offor on. If, however, the heat or other quantity under control is from avariable source, and the lag varies greatly at different times, thedevice as above described would cause rather slow approach to thecontrol point when lag was small. This can easily be overcome, to anydesired degree, by shortcircuiting a section of the control resistanceI8 at the control contact point. If, for example, the control resistanceis shorted between points 43 and 44 of Fig. 4 by a copper band and issuitably adjusted, the effect will be as indicated diagrammatically inFig. 7. The circuit will be balanced at 70 with contact I 8 touching anypart of the shorting band. If the temperature is rising so that the draglink tends to follow path a-b, and if line A represents the location ofthe shut-off contact in relation to the margins of the 70 band, thenwhen the drag pivot 9 reaches the edge of the band it must have not lessthan a certain lead angle to make shut-off contact. Shutoff before 70 isreached will take place only if the rate of temperature rise has beensufcient to make the drag link lead angle exceed this minimum value. Thesame will hold true if the temperature has been falling along the linec-d.

Referring to the approximate tractrx equation which has been given, itwill be noted that i,

the rate at which the lead angle decreases progressively becomes`smaller as the angle itself is decreased. By causing the contact at thecontrol temperature to be reached when the drag link and control contactangle are still appreciable, the rate at which control temperature isapproached under controlled conditionsv is substantially increased. Ifthis rate is below a minimum value,` which is determined by the Width ofthe resistance snorting band, in relation to other constants, noshut-off contact (or on contact, with falling temperature) will be madebefore the control temperature is reached, or at the exact controltemperature. When *his tornperature is passed by a very slight amount,hcwf* ever, the Contact i8 must cross the full '-.idth cf,

the s'norting band in order to balance theI circuit, and in so doingwill move contact I0 to 'turn heat on or olf as the case may be. Theresult is that, even when there is no lag in the heating system,

approach to control temperature follows paths as roughly indicated bythe broken lines of Fig. 8 instead of the slowly converging fulltractrix path of Fig. 2. It will be understood that in actual practicecertain minor errors of the instrument, combined with variations inrates of heating or cooling may cause divergence from theoreticalcurves, but the results are substantially as indicated. By varying thewidth of the shorting band on the control resistance the minimum rate,below which there willI be no anticipation, may be varied as desired. Bycentering the band to one side of the break between contacts I I and I2the minimum rate of approach from above may be made greater or less thanthat from below the control temperature.

I have discovered that a suitable apparatus, such as that abovedescribed, which employes what may be termed the tractrix principle, maybe eiectively employed in conjunction with other suitable accessoryapparatus to control temperature, acidity and many other variables, andwill automatically anticipate requirements to such extent that huntingof the type indicated in Fig. 1 is greatly reduced or eliminated.Changes from one control value to another, or return to a fixed controlvalue after sudden changes in demand, are made smoothly and quickly.Different types of self-balancing mechanism may obviously be used, andthe control characteristics may be altered within wide limits bysuitable design.v

Instead of using a self-balancing electrical circuit to control movementof the drag link pivot, 9 of Fig. 4, the latter may be attacheddirectly` to the mechanism of a liquid expansion thermometer, pressuregauge or other measuring device which will move it in similar manner. Inlack of a self-balancing circuit the rapid approach to control valuewhich has been described cannot be gained by means of a shorting band,but a closely similar effect may be gained by attaching firmly to themovable base I4 a second contact, under I0, whichgalso wipes plates Iland I2. As the angle of l swings from one side to the other the contactI0 must slide over the second contact. In so doing it makes electricalcontact with the latter, which at other times is electrically insulatedfrom the wire 34, and control contact with II and I2 is transferred tothe second contact spring which moves in direct relationto the change intemperature etc. under control.l By varying the width of the secondContact at the point where III touches and passes over it, and in sodoing is lifted from direct contact with II and I2, the band effectabove described may be almost duplicated.

This arrangement is shown in Figs. 9, 10 and 11. The lag and leadportions of the tractrix arm, 8 and I0 are shown as in Fig. 4, with thearm attached to pivot 9 in support I5 on the sliding base I4. Contact I8on resistance I9 in a self balancing circuit are shown, as above-described, but in this case equivalent results may be gained if theassembly mounted on sliding base I4 is moved, in responseto changes inthe variable, by other means. Also rigidly' attached to base I4 is anarm on which flexible contact 6I is mounted in such manner that itconstantly engages contact II or I2 and, unlike II), moves directly withthe pivot S. At 62 there is a widened portion or attachment to 6I, bentdownward at its extremities, over which the contact III must slide inswinging from one side to the other relative to 6I. In the top viewcontact I0 is shown at an angle to one side, engaging contact I2. In theside view contact I0 is shown lifted on 62 from contact I2 while at somelesser angle with or directly above 6I. The operation is as follows.

Assume that in a drop of temperature from above control level, forexample, contact swung to the lead angle shown to anticipate heatrequirement, engage I2 and turn on additional heat from the main supply.If control is only through I0, and there has been any excess ofanticipation, the tendency is for I0 to swing back and forth between I2and II as its pivot moves to the right, alternately turning on andshutting off heat and slowing approach to control temperature as itmakes decreasing angle with its neutraler mid position. With BI and 62mounted as shown, however, contact I0 remains in control only until itsangle with 6I decreases to a point where it starts to slide over 62 andin so doing is lifted from.I2 or II as the case may be. If, at themoment, IIJ has been engaging the on contact, I2, while 6I engages theoff contact II, control will be transferred from I0 through 62 and 6I toII, shutting oif the heat. So long as further change is at the same or alower rate there will be direct control through 6I without anticipation,expediting approach to control level. If the rate of change exceeds thepredetermined value it will cause I0 to move away from contact with 62and resume anticipating control.

One form of suitable assembly employing the foregoing in connection withregulation of temperature is for illustration further shown in Fig. 4.This assembly employs a temperature measuring and regulating devicefurther described and claimed in a separate application. A bi-metallicthermostat bar 50 is located at the point where temperature is to becontrolled. The bar 50 is mechanically adjusted so that at the -highesttemperature of the range through which anticipating regulating isdesired, its free end will lie between and be disengaged from the hightemperavture and low temperature contacts 54 and 53 respectively. Thelatter are connected to the two halves of the winding of solenoid 26,the circuit being completed, when bar 50 touches either contact, throughthe transformer 55 or other source of current and through conductor41-56. When the circuit through 54 is closed the lower ratchet dog 22engages gear 2I during each forward motion of the rocking support, andcauses screw I1 to move the base I4 and the assembly mounted on ittoward the left.

Many modifications of and additions to the tractrix mechanism arepossible, to gain specific desired effects. If, for example, it isdesired'to *gain regulation as described in connection with Fig. 4, butto set a predetermined maximum limit on the rate at which change maytake place, rate limit contacts may be mounted on the sliding pivotbase, I4, to be engaged by the drag arm in either direction when thepredetermined rate of change is exceeded. Figs. 17 and 18 show a form ofsuch limit contacts which may be used in an electrical control systemsuch as that of Fig. 4, the moving base I4, arms 8 and I0, pivot 9 etc.of the two figures corresponding. Attached to the base I4 and insulatedfrom each other except when in contact as will be described, are sixspring contact strips, numbers 66 to 'II inclusive. Attached to the freeends of 61 and 10 are rods of insulating material, 12 and 13, againstwhich the drag arm, 8, presses when the rate of change causes it toassume a suificient angle in one d1- 0 hasrection or the other. When arm8 is between these limit positions contact 61 engages contact 68 andcompletes the circuit 35-63 from off contact plate I I to the motor, asshown in Fig. 4. Contacts 68 and 'I0 similarly engage to complete the oncircuit. Under these conditions operation will be as previouslydescribed. If, for example, the temperature has been too high and startsto drop at more than the predetermined limit rate, before the fall hasbeen suiiicient to cause the anticipating arm, I8, to engage the oncontact, I2, then 8 will press against I2 and cause the circuit between61 and 68 to open while at the same time making contact between 61 and66. Since I8 is, under these conditions, in contact with II, the circuit65--ID-I I-35 to 64 will be closed and cause heat to be turned on tocheck the rate of temperature drop. Similar behavior, to turn oi heat,results in the case of too rapid an increase in temperature from belowcontrol level.

Means for regulating to a predetermined rate of change is shown in Figs.19 and 20. In this case, again, I4 and other similarly numbered partscorrespond to those of Fig. 4 except that terminals 35 and 36 aredisconnected from contact plates II and I2 and connected, respectively`to contact plates 'I5 and 'I4 attached to the moving pivot base I4. Aspring contact 16 attached to drag arm 8 engages one or the other ofthese contact plates and closes the corresponding circuits. If theopening between the contact plates is at one side of the center line, asshown, then the on circuit will be closed only when arm 8 makes an anglegreater than a with its mid position, and at any lesser angle, or if onthe other side, the off contact will be closed. Since contact of thedrag wheel on the revolving drum causes arm 8 to maintain angle a onlywhen the temperature is dropping at a denite rate it follows that withany departure from this rate on or oi contacts will be engaged asnecessary until the desired rate has been regained. It will beunderstood that the foregoing examples in connection with heating andcooling are for illustration only, and that with substitution ofequivalent apparatus it is possible to gain equivalent results in manyother types of control problem.

Many other Variations of design are possible. If lag. rather than leadof control is desired, the control contacts II and I2 etc. may be placedbetween 6 and 9. A variety of modiiications to meet special controlrequirements will be obvious, as will suitable accessories such as limitswitches to stop movement of I4 at either end of the screw I1.

Adjustment to different control Values may be gained in a Variety ofways, as by change in external resistance of the balancing circuit,movement of I3 and the attached contacts, or by dividing II and I2 intoa greater number of contact plates and changing the connections to theseplates as desired.

The foregoing descriptions have referred to control of heat etc. whencontrol only of full on or full 01T is required. In many applications itis desirable to have partial or complete proportioning of heat, alkaliilow, etc., to constantly balance the demand. The anticipating featuresof the tractrix control may be combined with proportioning devices withespecial advantage. Fig. 12 illustrates one form of suitable apparatus.The anticipating arm, I0, pivot 9, moving base I4 etc. are as previouslyillustrated and described.

A rod or cylinder of insulating material, l1, revolves constantly onshaft 18 mounted in fixed bearings. Mounted on the surface of 11 are twocontact areas, and 8|, of conducting material and so tapered that on oneside of 'I'I the conducting areas are adjacent and on the other side areappreciably separated, as indicated. Brushes 83 and 84 make continuouscontact with these two conducting areas and are in turn connected to thetwo halves, 85 and 86 of the divided field winding of a. motor forregulating the supply of heat or other variable under control, 81 beingthe commutator of the motor. When the variable is at the desired controllevel the tractrix contact arm I8 will lie in a position normal to theaxis of the proportioning switch cylinder, TI, and during eachrevolution of the latter will be continuously insulated from the motorcontacts, touching only the insulating area IIl--82. Any change fromcontrol level will cause arm I0 to move to one side and engage contacts8U or 8I during part of each revolution of l1, thereby causing theregulating motor to revolve in desired direction during the time of suchcontact. The time of contact during each revolution of TI, and resultantperiod of motor operation, progressively increases with increasingdeparture of I0 from the mid position, and consequently causes increasingly rapid change in corrective supply to the controlled variableas the amount and rate cf departure from control level increase. Sincethe motor is inoperative when arm I0 is in midposition, regardless ofits own position. stabilization will be gained when corrective supplyjust balances demand at the control level. The anticipation gained bymeans of the tractrix is especially desirable with this type ofproportioning mechanism, which otherwise tends to overrun badly.

Semi-proportioning, by turning supply on and oi during xed time cyclesfor periods the relative length of which are in proportion to demand,may be gained, together with anticipation, by using the tractrixmechanism with a revolving cylinder switch of the type illustrated inFig. 13. Operation is similar to the described above, but in this caseas the cylinder 88 revolves on shaft 89 the contact IO alternatelyengages conducting areas 90 and SI which are separated by insulatedspace 92. Motion of IIJ to the right of mid position increases thelength of periods during which the motor is turned in, say, on directionand decreases offi operation, and vice versa.

It is obvious that considerable latitude is permissible in shaping ofcontact areas and speed of switch revolution to meet specic conditions.

In many control devices now commonly used proportioning is gained by adouble potentiometer circuit, one part of which is varied in proportionto demand, and the other balanced by the response of the control motor,The tractrix control as first described and illustrated in Fig. 4 mayadvantageously be used in connection with such devices by substitutingthe motor control potentiometer resistance for the contacts II and I2 ofthat figure. Fig. 14 indicates the arrangement diagrammatically. Thenumbers correspond to those of Fig 4. a is for example a thermocouple, ba galvanometer relay controlling the selfbalancing potentiometer circuitI8, I9, etc. The position of contact arm IU of the tractrix unit on onehalf of the motor potentiometer circuit regulates the operation of theproportioning control motor through contact c which engages the otherportion of the motor control resistance, c

2. A regulating device employing the tractrix control principle,comprising an arm which is at one point connected by frictional contactwith a moving surface, is pivoted at another point which moves laterallyto but does not follow the motion of the surface in response to changesin value of the variable being controlled, and at another point orpoints which lead or lag behind the motion of the pivot point engagescontacts for regulation of the variable under control, all substantiallyas described.

3. An automatic regulating mechanism comprising an arm which is at onepoint connected by frictional contact with a moving surface, is atanother point attached to a pivot, the arm engaging one or moreregulating contacts at points which lead or lag behind the motion of thepivot, the pivot being connected to a contact with an electricalresistance in circuit with a device sensitive to changes in the value ofthe variable being regulated and also in circuit with means for causingthe pivot to move in one direction or the other lateral to the motion ofthe surface when the circuit is unbalanced, the circuit values beingsuch that change in value of the regulated variable will affect thesensitive element in such manner as to unbalance the circuit and causethe pivot and contact to move in the required direction and amount untilthe circuit is again balanced, a source of electrical current ofapproximately uniform potential, and a short circuiting band or widenedarea of uniform potential on the control resistance at the approximatepoint where the pivot contact touches when the circuit is balanced atthe desired value of the regulated variable.

4. An anticipatory regulating mechanism comprising an arm which is atone point connected by frictional contact with a moving surface, ispivoted at another point which is moved laterally to the motion of thesurface in response to changes in value of the variable being regulated,and at another point or points which lead or lag behind the lateralmotion of the pivot engages electrical contact means which regulatecompensation for departure of the variable from the desired condition, asecond contact arm which moves directly with the pivot and engages thesame regulating contacts, the second contact arm being disconnected fromthe electrical control circuit except at times when the pivoted arm isdirectly above such arm or makes less than a predetermined angle withsuch arm, and means whereby the pivoted arm is liftedl from directengagement with the regulating contacts and makes control contactindirectly through the second arm when the angle is less than apredetermined amount.

5. An anticipatory regulating mechanism comprising an arm which is atone point connected by frictional contact with a moving surface, ispivoted at another point which is moved laterally to the motion of thesurface in response to changes in value of the variable being regulated,and at another point or points which lead or lag behind the motion ofthe pivot engages contact means which regulate compensation fordeparture of the variable from desired condition, independent contactmeans which are mechanically connected to and move with the pivot beingprovided, and so located with respect to the pivotcd contact arm thatthey will be engaged when rate of change of the regulated variablecauses said arm to exceed a predetermined angle, said independentcontact means being connected to means for retarding rate of change ofthe regulated variable regardless of absolute value of such variable,until such time as the rate of change and angle of the pivoted contactarm have fallen below predetermined values.

6. A-rnechanism for regulating rate of change of a variable condition,comprising an arm which is at one point connected by frictional contactwith a moving surface, is pivoted at another point which is movedlaterally to the motion of the surface in response to changes in thevalue of the variable being regulated, and, at another point or pointswhich lead or lag behind the lateral motion of the pivot, engaging meansfor increasing or decreasing the value of the regulated variable, suchmeans being mechanically connected to follow the motion of the pivot,and so located with reference to the pivoted arm that they will beengaged by the latter at a predetermined angle and tend to cause thevalue of the regulated variable to increase or decrease at apredetermined rate.

7. An automatic system for regulating temperature, comprising acentrally pivoted arm which is in frictional contact with a movingsurface near one end and near the other end engages contacts to operatemechanism for increasing or decreasing'heat supplied from a main sourceto the regulated medium, motor driven means for moving the arm pivot inone direction or the other lateral to the motion of the surface, athermostatic element provided with contacts which actuate said means formoving the arm pivot when temperature of the thermostatic element isabove or below predetermined value, an electrical resistance heateradjacent and local to the thermostatic element, said heater being partlyin series and partly in parallel with a control resistance connectedacross a source of current through a variable contact mechanicallyconnected to the arm pivot, the relative values of heater and controlresistances being such that change in heat supplied to the thermostaticelement from the heater is substantially proportional to movement ofcontact on the control resistance, a shorting band or widened area ofuniform potential on the control resistance at the Contact positionapproximately corresponding to desired temperatures of the medium beingregulated, separate means actuated in conjunction with means forcontrolling heat from the main source whereby wattage of current flowingin the thermostat heater is increased Vin predetermined amount duringperiods when the main heat supply is turned on, clock controlled meansfor periodically and progressively varying wattage of thermostat heatercurrent through a predetermined range substantially independent of othercontrol adjustments, and separate clock controlled means for varying thethermostat heater current at desired times and in desired amounts, theseparate variations of heater current being eil'ected through variationsin the control resistance which is parallel with the heater, independentof the arm pivot contact with such resistance.

8. An automatic system for regulating temperature, comprising an arm atone point in frictional contact with a moving surface, and pivoted atanother point which moves in response to changes in the temperaturebeing regulated', a thermostatic element which engages electricalcontacts when the temperature of said element varies from predeterminedvalues, an electrical resistance heater adjacent and local to saidthermosatic element and-partly in series, partly in parallel through acontact mechanically connected to the arm pivot with a controlresistance connected across a source of current, motor operated meansactuated by the thermostat contacts to move the arm pivot and controlresistance contact as necessary to maintain the thermostatic element atapproximately constant temperature during changes in temperature of thesurrounding regulated medium, and contact means for increasing ordecreasing heat supplied to the regulated medium from a main source whensuch contacts are engaged by an extension of the pivoted arm at a pointwhich leads or lags behind motion of the pivot.

9. An automatic regulating device comprising an arm which is at onepoint connected by frictional contact with a moving surface, is pivotedat another point which is moved laterally to but does not' follow themotion of the surface in response to changes in value of the variablebeing regulated, and at another point or points which lead or lag behindthe motion of the pivot engages tapered contact areas on a revolvingproportioning switch, means being provided whereby the value of theregulated variable is progressively increased or 'decreased during thetimes of contact of said arm with one or the other contact areas.

10. An automatic regulating device comprising an arm which is at onepoint connected by frictional contact with a moving surface, is pivotedat another point which is moved laterally to but does not follow themotion oi the surface in response to changes in value of the variablebeing regulated, and at another point or points which lead or lag behindthe motion of the pivot engages a tapered contact area on a revolvingperiodic proportioning switch, means being provided whereby the value ofthe regulated variable is increased during times of contact of arm withsaid area and decreased at other times, or vice versa.

11. An anticipatory regulating mechanism comprising an arm which is atone point connected by frlctionai contact with a moving surface, ispivoted at another point which is moved laterally to the motion of thesurface in response to changes in value of the variable being regulated,and at another point or points which lead or lag behind the lateralmotion of the pivot engages contact means which regulate compensationfor departure of the variable from desired condition, a second contactarm which moves directly with the pivot and engages the same regulatingcontacts as the mst arm, the second contact arm being disconnected fromcontrol contact except at times when the pivoted arm makes less thanpredetermined angle with such arm, and means whereby the pivoted arm isdisengaged from control contact and control is transferred to the secondarm when the two arms make less than predetermined angle with eachother.

12. An automatic regulating device comprising an arm which is at onepoint connected by frictional contact with a moving surface, is atanother point attached to a pivot which may be moved laterally to themotion of said surface, said arm at one or more points which lead or lagbehind the lateral motion of said pivot engaging means to alter thecondition of the variable being regulated, a contact which moves inharmony with the lateral motion of said pivot and engages an electricalresistance in circuit with .a device sensitive to changes in value ofthe regulated variable, means whereby said circuit becomes balanced onlywhen the lateralposition of said pivot and said contact corresponds withthe value of the regulated variable, means whereby unbalance of saidcircuit causes corrective motion of pivot and contact until said circuitis balanced, while at the same time causing leading or laggingengagement of said pivoted arm with means which correctively alter thecondition of the regulated variable.

13. An anticipatory regulating mechanism comprising an arm which is atone point connected by frictional contact with a moving surface, ispivoted at another point which is moved laterally to the motion of thesurface in response to changes in value of the variable being regulated,and at another point or points which leador lag behind the lateralmotion of the pivot engages means which regulate compensation fordeparture of the variable from the desired condition, a second armwhich'moves in harmony with the pivot but is disengaged from regulatingmeans when rate of change and angle of the first arm exceedpredetermined minimum values and means whereby the second arm is causedto engage the regulating means when rate of change and angle of theiirst arm fall below predetermined values while first arm is at the sametime disengaged from the regulating means.

14. An automatic regulating device comprising an arm which is at onepoint connected by frictional contact with a moving surface, is pivotedat another point which is moved laterally to but does not follow themotion of the surface in response to changes in value of the variablebeing regulated, and at another point or points which lead or lag behindthe motion of the pivot engages an electrical resistance in the circuitwith proportioning means whereby the supply of corrective agent is madeto vary. in harmony with position of said arm on said resistance.

15. An automatic regulating device comprising an arm which is at onepoint connected by frictional contact with a moving surface, is pivotedat another point which ismoved laterally to but does not follow themotion of the surface in response to changes in value of the variablebeing regulated, and at vanother point or points which lead orlag behindthe motion of the pivot engages means which varies the supply of thecorrective agent, in proportion to the movement and position of thecontact arm at. the point of such engagement.

16. An automatic system for'regulating temperature comprising acentrally pivoted arm which is in frictional contact with a movingsurface nearrone end and near` the lother engages contact to operatemechanism for increasing or decreasing heat supplied from a main sourceto the regulated medium, motor driven means for moving the arm pivot inone direction or the other lateral to the motion of the surface, athermostatic element provided with contacts which actuate said means formoving the arm pivot when temperature of the thermostatic element isabove or below predetermined value, an electrical resistance heateradjacent and local to the thermostatic element, a source of current anda control resistance engaged by a contact moving in harmony with the armpivot whereby current flowing in the thermostat heater may be varied.

17. An automatic regulating device comprising a self-balancingelectrical circuit connected with means sensitive to changes in thevariable being regulated, means for anticipating changes in demand,substantially in proportion to rate of change, means whereby regulationis controlled substantially in proportion to such anticipated -demandwhen rate of change exceeds predetermined value, and a short circuitingband or widened area of uniform potential on the balancing resistancewhereby anticipation is cancelled and approach to control point isexpedited when rate of change and amount of departure fall belowpredetermined valuesl8 An automatic regulating s'ystem compris ing meanssensitive to change in value of the variable being regulated, connectedmeans which lead or lag behind changes in the true value of the variableby amounts which vary with the rate of change, connected means whichvary in direct harmony with changes in value of the regulated variable,and means whereby the leading or lagging element controls supply of thecorrective agent when rate of change exceeds predetermined values andmeans whereby the supply of the corrective agent is controlled by themember which moves in direct harmony with changes of the variable attimes when rate of change is less than predetermined value.

19. In measuring and control instruments, the combination with measuringmeans of a revolving drum, a wheel revolving in contact with said drum,means whereby said wheel is withheld from following the motion of thesurface of said drum but said wheel may follow its line of rollingContact lateral to said surface when the plane of said wheel is turnedat an angle to the line of motionvof said surface, and means responsiveto said measuring means whereby the angular deflection of the wheel andits motion lateral to the moving surface of the drum are guided inresponse to changes in value of the measured quantity.

20. In a regulating instrument, the combination with means responsive tochanges in value of the regulated quantity of a revolving drum, a wheelrevolving in contact with said drum, means whereby said wheel iswithheld from following the motion of the surface of said drum but mayfollow its line of rolling contact lateral to the motion of said surfacewhen the plane of said wheel is turned at an angle to the line of motionof said surface, means whereby said responsive means causes said wheelangle to change as necessary to cause the lateral motion of the wheelwith respect to the drum surface to approximately follow the direction,amount and rate of changes ir the regulated condition, means forapplying an agent to correct departure of the regulated condition fromdesired value, and means whereby during change in value of the regulatedcondition the application of the corrective agent is in part controlledas a function of the angle which said wheel is caused to take infollowing such change.

21. In a regulating instrument, the combination with means responsive tochanges in the regulated condition of a revolving drum, a wheel incontact with and revolving against said drum, a pivoted arm to whichsaid wheel and its supporting mount is suitably attached, meansconnected to said responsive means whereby the path of said Wheel onsaid drum is controlled as necessary to cause said arm to assume anangle which is a function of the rate of change taking place in theregulated condition, means for applying a corrective agent, and meanswhereby application of said corrective agent is in part a function ofthe angle assumed by said arm.

22. In a regulating instrument, the combina tion with means responsiveto changes in the regulated condition of a lever arm, means whereby onepoint on said arm is moved laterally from its median position inresponse to direction and amount of departure of the regulated conditionfrom desired value, means whereby said arm is angularly deflected aboutsaid point in response to the direction and rate at which change istaking place, means for applying a corrective agent, and means wherebyapplication of said corrective agent is controlled by the movement of asecond point on said arm.

23. In a regulating instrument, the combination of means responsive tochange in the regulated condition, means for applying a correctiveagent, a control member for regulating such corrective application,means whereby the movement and position of said control member is acontinuous function of the direction and amount of departure plus thedirection and rate of change during departure of the regulated conditionfrom desired value, and means whereby the movement and position of saidcontrol member is a continuous function of the direction and amount ofdeparture minus the direction and rate of change during return towarddesired value.

24. In measuring and control instruments, the combination with measuringmeans of a revolving drum, a wheel revolving in contact with said drum,means whereby said wheel is withheld from following the motion of thesurface of said drum but said wheel may follow its line of rollingcontact lateral to said surface when the plane of said wheel is turnedat an angle to the line of motion of said surface, means responsive tosaid measuring means whereby the angular deection of the wheel and itsmotion lateral to the moving surface of said drum are guided in responseto changes of value of the measured quantity, a pivoted lever arm, meanswhereby the pivot point of said arm is moved in response to changes invalue of the measured quantity, and means whereby said arm is angularlydeflected from a position normal to the line of motion of said pivot bythe angular deflection of said wheel during periods when the value ofthe measured quantity is changing.

25. In measuring and control instruments, the combination with measuringmeans of a revolving drum, a wheel revolving in contact with said drum,means whereby said wheel is withheld from following the motion of thesurface of said drum but said wheel may follow its line of rollingcontact lateral to said surface when the plane of said wheel is turnedat an angle to the line of motion of said surface, means responsive tosaid measuring means whereby the angular deflection of the wheel and itsmotion lateral to the moving surface of said drum are guided in responseto changes of value of the measured quantity, a pivoted lever arm, meanswhereby the pivot point of said arm is moved in response to changes invalue of the measured quantity, means' whereby said arm is angularlydeiiected from a position normal to the line of motion of said pivot bythe angular deflection of said wheel during periods when the value ofthe measured quantity is changing, means for applying a corrective agentto maintain or re-establish the desired value of the measured quantity,and means whereby application of said agent is controlled by movement ofa control point on said lever arm other than said pivot point from theposition at which said control point lies during periods when themeasured quantity has desired value and no change in value is occurring.

26. In measuring and control instruments, the combination with measuringmeans of a revolving drum, a wheel revolving in contact with said drum,means whereby said wheel is withheld from following the motion of thesurface of said drum but said wheel may follow its line of rollingcontact lateral to said surface when the plane of said wheel is turnedat an angle to the line of motion of said surface, means responsive tosaid measuring means whereby the angular deflection of the wheel and itsmotion lateral to the moving surface of said drum are guided in responseto changes of value of the measured quantity., a pivoted lever arm,means whereby the pivot point of said arm is moved in response tochanges in value of the measured quantity, means whereby said arm isangularly deflected from a position normal to the line of motion of saidpivot by the angular deflection of said wheel during periods when thevalue of the measured quantity is changing, means for applying acorrective agent to maintain or re-establish the desired value of themeasured quantity, means whereby application of said agent is controlledby movement of a control point on said lever arm other than said pivotpoint from the position at which said control point lies during periodswhen the measured quantity has desired value and no change in value isoccurring, and means whereby the application of said corrective agent isproportional to the movement of said control point -on said arm within apredetermined range.

27. In measuring and control instruments, the

combination with measuring means of a revolving drum, a wheel revolvingin contact with said drum, means whereby said wheel is withheld fromfollowing the motion oi' the surface of said drum but said wheel mayfollow its line of rolling contact lateral to said surface when theplane of said wheel is turned at an angle to the line of motion of saidsurface, means responsive to said measuring means whereby the angulardeection of the wheel and its motion lateral to the moving surface ofsaid drum are guided in response to changes of value of the measuredquantity, a pivoted lever arm, means whereby the pivot point of said armis moved in response to changes in value ofthe measured quantity, meanswhereby said arm is'angularly deflected from a position normal to theline of motion of said pivot by the angular deection of said wheelduring periods when the value of the measured quantity is changing,means for applying a corrective agent to maintain or re-establish thedesired value of the measured quantity, means whereby application ofsaid agent is controlled by movement of a control point on said leverarm. other than said pivot point from the position at which said controlpoint lies during periods when the measured quantity has desired valueand nochange in value is occurring, together with means whereby the rateat which said corrective application is increased or decreased is afunction of the amount of departure of said control point from theposition in which said control point lies when desired value exists andno change is taking place.

CLARK M. DENNIS.

